The present invention relates to a recording medium conveying device, especially to a recording medium conveying device for an ink jet printing device.
After a recording medium is printed by an ink jet printing device, such as an ink jet printer, an ink jet copy machine and an ink jet fax machine, the ink on the recording medium is still wet when being conveyed out of the ink jet printing device. If the recording medium is conveyed at the outlet by using two sets of rollers, chance is very much that the printed portions and the unprinted portions would be stained. The wet ink from the printed portion first taints the rollers, then the ink from the roller may in turn stain other printed portions and unprinted ones.
To counter this effect, besides quick-drying ink, the starwheel structure is also proposed. A starwheel has multiple tiny teeth on the rim. These teeth retain only infinitesimal amount of ink and hardly stain the recording medium. However, the tiny teeth on the edge of the starwheel tend to damage the recording medium due to the large local stress. Two of the structures disclosed in prior arts in order to maintain appropriate application of force on the recording medium are briefly described in the following paragraphs.
Please refer to FIG. 1(a). Brent et al, in U.S. Pat. No. 5,420,621, provides a structure of pinch wheels 101. Each pinch wheel 101 includes two connected starwheels mounted at the front end of a cantilever beam 102. At the back end of the cantilever beam 102 is placed a yoke 103. The yoke 103 receives the outer pin 104 located on the housing of a printing device and an L-shaped spring 105 provides appropriate force so that the pin on the pinch wheel would not pierce or damage the surface of the recording medium. A cantilever beam, a yoke, a pinch wheel and a spring are required to be correctly assembled. The pinch wheel, however, may demand some special assembly efforts and thus the assembly rate and productivity are downgraded.

Please refer to FIG. 1(b). In U.S. Pat. No. 5,606,357 invented by Toshihiko Bekki et al, a spur 107 supported by a coil spring 106 is disclosed. The spur 107 has a structure similar with the starwheel. Compared with the prior art described above, the most significant change is that Toshihiko adopted the coil spring 106. The elasticity of the coil spring 106 provides adequate force on the double starwheels so that the teeth on the double starwheels would not pierce or damage the surface of the recording medium. Though being creative on using the coil spring as the shaft, however, the coil spring is apt to fall apart when rolling. Moreover, owning to the small size and enforcement on both sides of the coil spring, the assembly process is inefficient and difficult.
In order to straighten out all those defects in the prior arts depicted above, the present invention proposes a recording medium conveying device. In one embodiment of the present invention, a cantilever beam integral with the ink jet printing device is adopted. The cantilever beam is provided with multiple supporting device and a stress concentration zone. The cantilever beam, by employing its elasticilty, holds a starwheel mounted at one end of the cantilever beam and a recording medium in contact and maintains the intactness of the recording medium. The stress concentration area limits the stress within area. In the first preferred embodiment, since the cantilever beam is integrated with the housing, the structure is well constructed after the starwheel is in place.
On the other hand, in the second preferred embodiment of the present invention, an elastic connective connects a star ring and a shaft to form a rotatable starwheel. The elastic connective holds the starwheel and the recording medium in appropriate contact without damaging the recording medium, even if the mount (eg. the cantilever beam) is substantially rigid.
The two embodiments are ready for combination to form a double-elastic structure having both an elastic cantilever beam and an elastic connective.